Intraspecific variation in seed dispersal between annual and perennial populations

Seed dispersal impacts plant fitness by shaping the habitat and distribution of offspring, influencing population dynamics and spatial genetic diversity. Whether the evolution of dispersal strategies varies across herbaceous life forms (annual, perennial or clonal) is unresolved. In this study, we examine how seed-dispersal strategies vary between annual and perennial populations of Mimulus guttatus (syn. Erythranthe guttata), investigating differences in seedpod orientation and shape and in the probability and distance of seed dispersal.

We conducted a greenhouse experiment using 190 plants from six populations of annual and perennial M. guttatus, to compare floral orientation, seedpod architecture and its effect on seed dispersal. We used controlled wind trials to measure the probability of seed dispersal and the dispersal distance of individual seeds from plants.

We identify the following three key differences in seedpod architecture and seed dispersal in annuals and perennials: seedpods are angled more upward-facing in perennials compared with annuals; a lower proportion of seed is dispersed in perennials; and seeds disperse further in perennials than in annuals. These results are consistent with our predictions that a clonal, perennial life form should be associated with traits that increase the retention of seeds, requiring greater wind speeds to dislodge seed and increasing dispersal distance.

Despite the close genetic relationship between annual and perennial populations of M. guttatus, we find differences in seedpod architecture and seed dispersal. We suggest that perennial plants, characterized by clonal reproduction and multi-year survival, benefit from strategies that facilitate long-distance seed dispersal to mitigate competition and promote colonization of new habitats.